Flexible laminate for printed-circuit boards are materials for the fabrication of printed circuits having flexibility, and their use is increasing in recent years, for example, because the cases for containing printed circuits are being reduced in size. Conventionally, such flexible laminate for printed-circuit boards have been made by bonding a polyimide film to copper foil with the aid of an adhesive. In such boards, the polyimide film has satisfactorily good heat resistance, electrical properties and mechanical properties, but the adhesive has inadequate properties. For this reason, they have had the disadvantage that the good properties of the polyimide film are not fully utilized.
Accordingly, attempts have been made in the prior art to form a flexible laminate for printed-circuit board comprising a metal-clad polyimide sheet, without the aid of an adhesive. Some examples are disclosed in U.S. Pat. No. 3,179,634, Japanese Patent Laid-Open Nos. 129862/'74, 190091/'83 and 190092/'83, and the like. However, a flexible laminate for printed-circuit board having a combination of adequate heat resistance, adhesion strength and flexibility has not yet been provided.